Caveat: sadly I am far from an expert on CMake. Yes, this is a strange problem. I have not been able to reproduce it here (Ubuntu, full portaudio install). I am assuming you are using the latest code set from github.
It does seem that CMake can get in a bit of a muddle, and the time-honoured solution has been to delete the whole CMakeFiles directory (in the 'paplay" directory inside the main 'build' directory set up before running Cmake for the first time). This will force CMake (when you run 'make' in the build directory) to reconstruct all the internal config files, reading CMakeLists.txt to do so. You can inspect CMake's record of all target include files by checking the file CMakeFiles/paplay.dir/paplay.c.o.d. A quick way to reach this is using 'grep' recursively in, say, the paplay directory:
grep -R pa_ringbuffer .
Alternatively, run this from the build directory itself, which should find the instances for recsf, paplay, pvplay (four source files in all).
It is also useful to remember that you can run 'make' on a single target program to check it (e.g.: 'make paplay'), no need to run through the whole program set each time.
